The BBC's Karen Allen: "One third of pregnant woman continue to smoke"

It estimates that 200,000 - one in three - pregnant women continue to smoke, despite a wealth of evidence showing the habit can damage the unborn child.

And the number has been going up in the last seven years.

The research, from the Health Education Authority (HEA), shows that the main reasons women continue to smoke during pregnancy are stress and addiction.

The study was published on Tuesday as Public Health Minister Tessa Jowell launched a new "No Tar! Mum" advertising campaign to encourage women to quit.

Miscarriage risk

Smoking during pregnancy has been shown to harm both the unborn child and the mother.

The mother is more likely to vomit, get urinary infections and to feel unwell if she smokes during pregnancy.

Cot death is associated with smoking during pregnancy, the risk of miscarriage is increased by 27% and the baby is more likely to develop respiratory illness.

Dr Lesley Owen, senior research manager at the HEA, said: "The dangers of smoking during pregnancy are now well established.

"But it really is never too late to give up smoking - even stopping in the final months of your pregnancy will help your baby."

Quit rates

The survey covers the period between 1992 and 1997, and looks at the attitudes and behaviour of smokers.

It found that of women who smoked:

• 10% stopped immediately before getting pregnant
• One in five kicked the habit at some point during pregnancy
• 4% cut down before they found they were expecting
• 33% cut down during pregnancy
• 19% of former smokers relapsed during pregnancy

Campaign details

The government's advertising campaign will consist of radio and television commercials and a poster campaign, which will track the growth of a foetus.

In the sixth week, the poster reads: "He already has a brain, a spine and nicotine in his system. Help him quit before he's born."

"Giving up smoking is probably the best single thing you can do for your baby's health," Ms Jowell said.

"It is estimated that every year more than 400 babies are stillborn, or die soon after birth, because their mothers smoke."

She said the government's White Paper on smoking aimed to reduce the number of women smoking during pregnancy to 15% by 2010, so it was alarming that the figure was still so high.

Men's responsibility

Clive Bates, director of Action on Smoking and Health, said that although the dangers of smoking during pregnancy were well documented, they were not always communicated as forcefully as they could be.

Health professionals may fear confrontation with people they wanted to help, he said.

And pregnant women were not the only ones with the responsibility to stop.

"Men have got a huge amount to answer for," he said. "We know that although many women try to give up smoking during pregnancy, they are not helped by partners who do not.

"It is incredibly difficult to give up when there's somebody sitting next to you smoking.

"If more men gave up, then more women would be able to give up smoking."

But a spokesman for FOREST, the pro-smoking organisation, accused the HEA of "hounding" pregnant women to give up smoking.